The expression of rRNA genes from Drosophila is being studied with the primary aim of understanding the cause for the inactivity of interrupted genes. Run-off transcription in isolated nuclei of Drosophila cells showed that insertions are not transcribed in vitro; thus isolated nuclei preserve in vivo control in this respect. Polymerase loading on regions upstream and downstream of the insertion was measured, leading to the suggestion that interrupted rRNA genes are transcribed up to the point of insertion but not beyond. Preliminary experiments were carried out towards studying rDNA transcription in a reconstituted system.